X DPI Setting – Is It Only for Text Scaling?

dpignu-screenresolutionx11

On Linux the DPI (dot per inch) is set to 96 per default, it can be changed globally on the X start up parameter for instance X -dpi 120

This seem to mainly impact text/font scaling. In comparison when screen resolution (ex 1920×1080) is changed this impact everything (window/text/image/etc).

Is DPI meant only for text scaling?

Best Answer

DPI

DPI stand for dots per inch and is a measure of spatial printing/display, in particular the number of individual dots that can be placed in a line within the span of 1 inch (2.54 cm). Computer's screens do not have dots, but do have pixels, the closely related concept is pixels per inch or PPI and thus DPI is implemented with the PPI concept. The default 96 DPI mesure mean 96x96 vertically and horizontally. Additionally What is DPI and when does it matter? video is very informative.

Resolution

A native screen resolution, represent the number of pixels (X,Y horizontally and vertically) that a screen have physically. For instance a Full HD screen 1920x1080 have a count of 1920 physical pixel horizontally and a count of 1080 physical pixel vertically which mean 2073600 pixels in total for the whole screen.
Compared to the DPI (dots per inch), the resolution is not linked at all to a physical size measurement but is just an horizontal/vertical pixel count.

Xorg, DPI and Resolution

The X server needs, gets and uses the real/guessed screen spatial measurement along with its resolution in order to implement the DPI/PPI feature. On a desktop configuration we do use a screen resolution and a DPI/PPI value, each displayed element (text, application, etc) does implement a sizing mechanism to display its content, most of the time pixels are used this is why the DPI setting does not impact most windows size, because they are implementing a pixel measurement not DPI. On the other hand text/font does implement the DPI/PPI measurement and their size get changed when the DPI value is changed.

Commands and configuration

Changing the DPI with SDDM:

# Edit /etc/sddm.conf with the following
[X11]
ServerArguments=-nolisten tcp -dpi 120

Changing the DPI with Lightdm:

# Edit /etc/lightdm/lightdm.conf.d/lightdm.conf with the following 
[SeatDefaults]
xserver-command=X -dpi 120

Get the current DPI

xdpyinfo | grep dots
xrdb -query | grep dpi

Get the screen measurement

# Note that xrandr Xorg extension does not display an accurate measurement  
xrandr | grep -w connected
# alternative
xdpyinfo | grep -B2 resolution

Get an accurate screen measurement (sudo/root required)

monitor-edid
# or
monitor-edid | monitor-parse-edid
# or
get-edid | parse-edid

Links: 1, 2, 3

Related Solutions

Linux – How to zoom into the desktop but maintain high resolution for fonts etc

Hi fellow Awesome WM user! I have had this same issue and found out that Awesome WM currently does not support dpi scaling. So that means we are on our own. A lot of applications pick up the dpi from X server. So make sure your X server has the right dpi (several ways: Xorg conf monitor size, .Xresources, cal xrandr with dpi flag...).

Best solution I found until now: just use a large font-size.
You can also increase the sizes of the menu's and other elements that you find too small.

Wayland is not an option if you want to keep using Awesome WM because it implements the X server api, wayland is something different.

IIRC compton is also not going to help because it doesn't help you with scaling acording to dpi.

Larger “xterm” fonts on HIDPI displays

You have hinted the answer yourself by referencing https://en.wikipedia.org/wiki/Fixed_(typeface)

This is the standard fixed bitmap font which has been expanded by Markus Kuhn to have a rather complete character set. The question is then how to scale a bitmap.

What you have achieved so far is scaling a vector font and converting it to a bitmap (ttf → bdf → pcf). That is a fine strategy but as you mention it lacks some language support. That seems strange as Courier New is one of the more unicode complete fonts but I digress! Maybe try using Mono which is a clone.

I do however not understand why you are doing this as xterm does support truetype.

Modify ~/.Xresources such as this (note that you'll need to reload it using xrdb as seen in another answer to this question):

XTerm*renderFont: true
XTerm*faceName: VeraMono
XTerm*faceSize: 10

But back to the task: You want a larger bitmap font.

The largest available bitmap available is:

10x20   -Misc-Fixed-Medium-R-Normal--20-200-75-75-C-100-ISO10646-1

Markus have been so nice that he supplies the source BDF files. If your distribution does not have the most recent updates (from April 2009) you can grab the package directly from him.

The "-misc-fixed-*" font package:

http://www.cl.cam.ac.uk/~mgk25/download/ucs-fonts.tar.gz

Rather than converting back and forth between pcf and bdf you could/should stick to the source format. You can use a BDF font editor to resize the font. Do not expect any antialiasing or such trickery - but at least you can get a readable size.

Or you can use bdfresize by Hiroto Kagotani (also found in some package systems).

UPDATE:

I do not know of a way to scale just one window (never had the need). You could track this Superuser question. When I have had the need I have scaled the entire environment.

You can downgrade a 3200x1800 display to 1920x1080 using:

xrandr --dpi 141
xrandr --output eDP1 --scale 0.6x0.6

Other tricks for screen scaling in different window managers can be found here. They suggest using VNC:

One approach is to run the application full screen and without decoration in its own VNC desktop. Then scale the viewer. With Vncdesk (vncdesk-git from the AUR) you can set up a desktop per application, then start server and client with a simple command such as vncdesk 2.

x11vnc has an experimental option -appshare, which opens one viewer per application window. Perhaps something could be hacked up with that.